![]() ![]() It tends to cause pain, skin rashes, fever and muscle cramps. Although a jellyfish can kill a small aquatic animal, its sting is not usually fatal to humans. The venom is a neurotoxin designed to paralyze jellyfish prey. The stinging cells spring out at the unwitting victim like tiny darts, firing venom into it. ![]() When a jellyfish encounters another object, pressure inside the nematocyst causes the threads to uncoil. Their sting is both a defense mechanism and a way to capture their prey.Įach jellyfish tentacle is covered with thousands of cells called cnidoblasts, which house nematocysts containing stinging threads. They don't seek out people to attack - their nervous system is too simple to do that. Larger jellyfish eat crustaceans and other bigger aquatic animals. Smaller jellyfish eat algae and other tiny plankton called zooplankton. Jellyfish are carnivores - they eat other animals. To see light, detect smells and orient themselves, they have rudimentary sensory nerves at the base of their tentacles.Ī jellyfish's body generally comprises six basic parts: Jellyfish have very simple bodies - they don't have bones, a brain or a heart. If you cut a jellyfish in half at any point, you'll always get equal halves. Their bodies have radial symmetry, which means that the body parts extend from a central point like the spokes on a wheel. If a jellyfish washes up on the beach, it will mostly disappear as the water evaporates. The jellyfish's cnidarian relatives include corals, sea anemones and the Portuguese man-o'-war. All cnidarians have a mouth in the center of their bodies, surrounded by tentacles. Jellyfish are also members of the phylum Cnidaria, (from the Greek word for "stinging nettle") and the class Scyphozoa (from the Greek word for "cup," referring to the jellyfish's body shape). Jellyfish can range in size from less than an inch to nearly 7 feet long, with tentacles up to 100 feet long. Some plankton are microscopic, single-celled organisms, while others are several feet long. These plants and animals either float in the water or possess such limited swimming powers that currents control their horizontal movements. Jellyfish live mainly in the ocean, but they aren't actually fish - they're plankton.
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